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<a name="Output"></a>
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<p>
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<hr>
<a name="Commands-for-Controlled-Output"></a>
<h4 class="subsection">23.1.4 Commands for Controlled Output</h4>

<p>During the execution of a command file or a user-defined command, normal
<small>GDB</small> output is suppressed; the only output that appears is what is
explicitly printed by the commands in the definition.  This section
describes three commands useful for generating exactly the output you
want.
</p>
<dl compact="compact">
<dd><a name="index-echo"></a>
</dd>
<dt><code>echo <var>text</var></code></dt>
<dd><p>Print <var>text</var>.  Nonprinting characters can be included in
<var>text</var> using C escape sequences, such as &lsquo;<samp>\n</samp>&rsquo; to print a
newline.  <strong>No newline is printed unless you specify one.</strong>
In addition to the standard C escape sequences, a backslash followed
by a space stands for a space.  This is useful for displaying a
string with spaces at the beginning or the end, since leading and
trailing spaces are otherwise trimmed from all arguments.
To print &lsquo;<samp>&nbsp;<!-- /@w -->and foo =&nbsp;<!-- /@w --></samp>&rsquo;, use the command
&lsquo;<samp>echo \&nbsp;<!-- /@w -->and foo = \&nbsp;<!-- /@w --></samp>&rsquo;.
</p>
<p>A backslash at the end of <var>text</var> can be used, as in C, to continue
the command onto subsequent lines.  For example,
</p>
<div class="smallexample">
<pre class="smallexample">echo This is some text\n\
which is continued\n\
onto several lines.\n
</pre></div>

<p>produces the same output as
</p>
<div class="smallexample">
<pre class="smallexample">echo This is some text\n
echo which is continued\n
echo onto several lines.\n
</pre></div>

<a name="index-output"></a>
</dd>
<dt><code>output <var>expression</var></code></dt>
<dd><p>Print the value of <var>expression</var> and nothing but that value: no
newlines, no &lsquo;<samp>$<var>nn</var> = </samp>&rsquo;.  The value is not entered in the
value history either.  See <a href="Expressions.html#Expressions">Expressions</a>, for more information
on expressions.
</p>
</dd>
<dt><code>output/<var>fmt</var> <var>expression</var></code></dt>
<dd><p>Print the value of <var>expression</var> in format <var>fmt</var>.  You can use
the same formats as for <code>print</code>.  See <a href="Output-Formats.html#Output-Formats">Output
Formats</a>, for more information.
</p>
<a name="index-printf"></a>
</dd>
<dt><code>printf <var>template</var>, <var>expressions</var>&hellip;</code></dt>
<dd><p>Print the values of one or more <var>expressions</var> under the control of
the string <var>template</var>.  To print several values, make
<var>expressions</var> be a comma-separated list of individual expressions,
which may be either numbers or pointers.  Their values are printed as
specified by <var>template</var>, exactly as a C program would do by
executing the code below:
</p>
<div class="smallexample">
<pre class="smallexample">printf (<var>template</var>, <var>expressions</var>&hellip;);
</pre></div>

<p>As in <code>C</code> <code>printf</code>, ordinary characters in <var>template</var>
are printed verbatim, while <em>conversion specification</em> introduced
by the &lsquo;<samp>%</samp>&rsquo; character cause subsequent <var>expressions</var> to be
evaluated, their values converted and formatted according to type and
style information encoded in the conversion specifications, and then
printed.
</p>
<p>For example, you can print two values in hex like this:
</p>
<div class="smallexample">
<pre class="smallexample">printf &quot;foo, bar-foo = 0x%x, 0x%x\n&quot;, foo, bar-foo
</pre></div>

<p><code>printf</code> supports all the standard <code>C</code> conversion
specifications, including the flags and modifiers between the &lsquo;<samp>%</samp>&rsquo;
character and the conversion letter, with the following exceptions:
</p>
<ul>
<li> The argument-ordering modifiers, such as &lsquo;<samp>2$</samp>&rsquo;, are not supported.

</li><li> The modifier &lsquo;<samp>*</samp>&rsquo; is not supported for specifying precision or
width.

</li><li> The &lsquo;<samp>'</samp>&rsquo; flag (for separation of digits into groups according to
<code>LC_NUMERIC'</code>) is not supported.

</li><li> The type modifiers &lsquo;<samp>hh</samp>&rsquo;, &lsquo;<samp>j</samp>&rsquo;, &lsquo;<samp>t</samp>&rsquo;, and &lsquo;<samp>z</samp>&rsquo; are not
supported.

</li><li> The conversion letter &lsquo;<samp>n</samp>&rsquo; (as in &lsquo;<samp>%n</samp>&rsquo;) is not supported.

</li><li> The conversion letters &lsquo;<samp>a</samp>&rsquo; and &lsquo;<samp>A</samp>&rsquo; are not supported.
</li></ul>

<p>Note that the &lsquo;<samp>ll</samp>&rsquo; type modifier is supported only if the
underlying <code>C</code> implementation used to build <small>GDB</small> supports
the <code>long long int</code> type, and the &lsquo;<samp>L</samp>&rsquo; type modifier is
supported only if <code>long double</code> type is available.
</p>
<p>As in <code>C</code>, <code>printf</code> supports simple backslash-escape
sequences, such as <code>\n</code>, &lsquo;<samp>\t</samp>&rsquo;, &lsquo;<samp>\\</samp>&rsquo;, &lsquo;<samp>\&quot;</samp>&rsquo;,
&lsquo;<samp>\a</samp>&rsquo;, and &lsquo;<samp>\f</samp>&rsquo;, that consist of backslash followed by a
single character.  Octal and hexadecimal escape sequences are not
supported.
</p>
<p>Additionally, <code>printf</code> supports conversion specifications for DFP
(<em>Decimal Floating Point</em>) types using the following length modifiers
together with a floating point specifier.
letters:
</p>
<ul>
<li> &lsquo;<samp>H</samp>&rsquo; for printing <code>Decimal32</code> types.

</li><li> &lsquo;<samp>D</samp>&rsquo; for printing <code>Decimal64</code> types.

</li><li> &lsquo;<samp>DD</samp>&rsquo; for printing <code>Decimal128</code> types.
</li></ul>

<p>If the underlying <code>C</code> implementation used to build <small>GDB</small> has
support for the three length modifiers for DFP types, other modifiers
such as width and precision will also be available for <small>GDB</small> to use.
</p>
<p>In case there is no such <code>C</code> support, no additional modifiers will be
available and the value will be printed in the standard way.
</p>
<p>Here&rsquo;s an example of printing DFP types using the above conversion letters:
</p><div class="smallexample">
<pre class="smallexample">printf &quot;D32: %Hf - D64: %Df - D128: %DDf\n&quot;,1.2345df,1.2E10dd,1.2E1dl
</pre></div>

<a name="index-eval"></a>
</dd>
<dt><code>eval <var>template</var>, <var>expressions</var>&hellip;</code></dt>
<dd><p>Convert the values of one or more <var>expressions</var> under the control of
the string <var>template</var> to a command line, and call it.
</p>
</dd>
</dl>

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